"""
Copyright 2022 Google LLC
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
    http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
"""
# [START drive_fetch_changes]

from __future__ import print_function

import google.auth
from googleapiclient.discovery import build
from googleapiclient.errors import HttpError


def fetch_changes(saved_start_page_token):
    """Retrieve the list of changes for the currently authenticated user.
        prints changed file's ID
    Args:
        saved_start_page_token : StartPageToken for the current state of the
        account.
    Returns: saved start page token.

    Load pre-authorized user credentials from the environment.
    TODO(developer) - See https://developers.google.com/identity
    for guides on implementing OAuth2 for the application.
    """
    creds, _ = google.auth.default()
    try:
        # create gmail api client
        service = build('drive', 'v3', credentials=creds)

        # Begin with our last saved start token for this user or the
        # current token from getStartPageToken()
        page_token = saved_start_page_token
        # pylint: disable=maybe-no-member

        while page_token is not None:
            response = service.changes().list(pageToken=page_token,
                                              spaces='drive').execute()
            for change in response.get('changes'):
                # Process change
                print(F'Change found for file: {change.get("fileId")}')
            if 'newStartPageToken' in response:
                # Last page, save this token for the next polling interval
                saved_start_page_token = response.get('newStartPageToken')
            page_token = response.get('nextPageToken')

    except HttpError as error:
        print(F'An error occurred: {error}')
        saved_start_page_token = None

    return saved_start_page_token


if __name__ == '__main__':
    # saved_start_page_token is the token number
    fetch_changes(saved_start_page_token=209)
# [END drive_fetch_changes]
